The present invention generally relates to a temperature controller and more particularly, to a temperature control device arranged to control temperature of an object to be controlled through variation of on/off ratio for control output of an output control section, i.e. output ratio.
Conventionally, there has been proposed a temperature control device for controlling temperature of an object to be controlled, which is so arranged that, based on the temperature of the object to be detected and a target value to be set, predetermined calculations are effected by an operation or calculation unit at each sampling period so as to vary the on/off output ratio of an output control section according to the result of the above calculations for applying the output control amount thereof to the object to be controlled, thereby to control the temperature of said control object. In the known temperature control device of the above described type, when a relay or the like which is required to be relatively low in the number or frequency for opening and closing is employed for the output control section, it has been a common practice, as shown in FIGS. 1(a) to 1(d) that, with respect to sampling periods comparatively small in length (i.e. S1, S2, . . . , and S16 in FIG. 1(a)), on/off control is effected by proportional periods each having a length several times that of the sampling period (i.e. T1, T2, . . . and so forth in FIG. 1(c)). More specifically, the calculation of output ratio at the operation unit is effected per sampling period so as to obtain the output ratio at each time (O1, O2, . . . , and O16 in FIG. 1(b)), and the output ratio at each of the sampling periods is summed up during the proportional period (for example, addition for O1+O2+ . . . O8 is effected during the proportional period T1) so that the relay is energized or turned on in the subsequent proportional period (e.g. the proportional period T2) by an period equivalent to the added ratio (FIG. 1(d)). In the case where the frequency or number of opening and closing is required to be reduced as in the relay and the like, it may be unavoidable to effect the open/close function at a proportional period several times longer than that of the sampling period, if the sampling period is small, but in such a case, the functioning of the relay or the like corresponding to the temperature variation is inevitably delayed by one proportional period, thus being unable to keep up with the temperature variation when a load response speed of the object to be controlled is high, and consequently, stable control can not be effected as intended.